My iPhone 4S always showed a notification in banner (that is, the top of the iPhone screen) when a new message/mail came to me. Those notifications can be viewed in any state(Means, Even if I am playing a game or I am seeing some other apps, I can see the notification in the banner if a new message came).

But, the problem that I faced is, nowadays, it doesn't show the notifications on the banner. If a new message appears, it just show the notification on Messages app icon with the corresponding badge value. Also, I opened the notification screen (by swiping from the top of the screen), the notification appears.

The problem is, it does not show the new message alert in the banner. I attached my Messages app's notification settings here.